Most sinograms (i.e., Chinese characters) are phonograms (phonetic compounds). A phonogram is composed of a semantic radical and a phonetic radical, with the former usually implying the meaning of the phonogram, and the latter providing cues to its pronunciation. This study focused on the sub-lexical processing of semantic radicals which are themselves free standing sinograms. Two primed naming experiments were carried out to examine whether the meanings and pronunciations of the semantic radicals embedded in phonograms were activated or not during sinogram recognition. In Experiment 1, semantically opaque phonograms were used as primes. We observed facilitatory priming effects for targets which were semantically related to the semantic radicals embedded in primes, but not to the primes themselves. These effects were present for low-frequency primes, but not for high-frequency primes. Experiment 2 used only low-frequency phonograms as primes. We observed facilitatory priming effects for targets which were homophones of the semantic radicals embedded in primes, but not of the primes themselves. These results suggest that sub-lexical semantic and phonological information of semantic radicals are activated, and that the activation processes are modulated by the lexical frequency of the host phonograms. Our study shows that sub-lexical processing of semantic radicals is similar to that of phonetic radicals, indicating no fundamental difference between sub-lexical processing of semantic and phonetic radicals, supporting the view that a radical has a unique representation irrespective of its function in the orthographic system of Taft's model.